This invention relates to novel homogeneous catalyst formulations for methanol production. These new formulations have a number of features: liquid phase performance, low temperature, low pressure performance, high activity, and high selectivity, which permits gas conversions in one pass through greater than 90%, and under optimum conditions gas conversions of about 97%. Since this catalyst system is a liquid phase system, it permits the reaction between carbon monoxide and hydrogen to form methanol, which is an exothermic reaction, to proceed at fully isothermal conditions. In contrast, the traditional pelleted, solid catalysts used in methanol production create hot spots in the reactor which prevent the process from operating efficiently. Further, because the homogeneous catalyst is in solution, reaction heat removal can be decoupled from kinetics. Thus, unlike existing processes, with the instant process optimum performance, both chemically and thermally, can be built into the production system separately, with the components of the production system designed to optimize heat removal and kinetics.
The homogeneous catalyst formulation of the present invention overcomes other disadvantages of conventional, solid-phase, methanol synthesis catalysts. Typically, conventional processes require high temperatures (250.degree. C.) and high pressure (765 psi) and are limited by low equilibrium conversion (60%). Using the catalysts of the present invention, methanol production can be conducted at low temperatures and pressure with a high equilibrium conversion.
Further, conventional type catalysts, such as pellet type catalysts, usually exhibit a gas conversion rate of about 16-30% per pass, necessitating the re-cycling of the feed gas in order to operate the production system at an economically acceptable efficiency. Thus, although partial oxidation of natural gas yields an ideal methanol feed gas, partial oxidation cannot be used to produce the feed gas for conventional catalyst systems because such systems require a feed gas with very low levels of inert gases, especially nitrogen. Inerts such as nitrogen that build up in the recycle stream must be kept low for process efficiency. To produce feed gases with low levels of inerts, the partial oxidation would have to be carried out using oxygen and this approach renders this method of feed gas preparation economically unfeasible. The instant catalyst system makes it possible to take advantage of partial oxidation production of the synthesis feed gas because the high conversion eliminates the need for a recycle stream and thereby permits use of air rather than oxygen, saving the large costs for oxygen generation. A further improvement that results from the high efficiency of the process that permits one pass through operation is that the atmospheric nitrogen that enters the system through the air partial oxidation step leaves the reactor at reaction pressure and can be expanded to provide energy, for example for air compression.
The present invention provides a homogeneous catalyst that permits the production of methanol from a synthesis gas feed gas containing inert gases, at low temperatures and pressures and at high gas conversion rates. This represents a significant improvement in reaction conditions and process efficiency over the conventional methanol catalysts.